Solar installation

ABSTRACT

The solar installation ( 10 ) according to the invention having a collector array (K) and a heat storage container ( 20 ) has a drain-back holding device ( 24 ) which is integrated with a heat exchanger ( 22 ), which is located in the container ( 20 ), in that its upper area has an expansion and return volume. It is preferably in the form of an integral pipe coil (R), which is a smooth-pipe helix with a uniform gradient. Furthermore, a second heat exchanger ( 34 ) can be arranged, coaxially with respect to it. The pipe coil (R) has means, at least in the lower area, for reducing the free flow cross section in the pipe interior ( 32 ), specifically cylindrical or profiled, fixed or moving filling bodies ( 30 ) which, for example, are individual bodies, which are closed at the end, with a standard form which promotes swirling, and/or which may be composed of a material of high thermal capacity, such as steel, stone, ceramic or the like.

The invention relates to a solar installation as claimed in the preambleof claim 1.

Typical solar installations have at least one solar collector which, forexample, is arranged on a house roof and is connected via pipelines to aheat store. This is in general a vertical service-water tank, whichcontains a heat exchanger in the form of a pipe coil. In practice, thetemperature is measured directly at the store, for example in the lowerarea of the solar heat exchanger. A pump which is arranged in the returnline can be controlled as a function of the instantaneous temperaturedifference from the collector temperature.

If the solar radiation is sufficient, a regulator activates the pump,such that the medium which is located in the lines—generally water withantifreeze—circulates, thus transporting the heat absorbed by thecollector into the tank. If the solar heat is not sufficient, then thepump is switched off, in which case the water located in the store canbe raised to a desired temperature by conventional heating means, forexample via a second heat exchanger. If overheating occurs, for examplein hot summer or in the event of an electrical power failure, it isnecessary to prevent solar liquid from being lost as a result of excesspressure. By way of example, a safety valve of suitable design is usedas a self-protection device for this purpose.

In order to save physical components, for example a membrane expansionvessel, and also to allow heat carriers to be used without antifreeze,drain-back systems have been developed which allow the heat carriermedium to be fed back into a collecting container when the pump is notrunning, the inlet side of which collecting container is generallylocated upstream of the heat storage container. The emptied collectornow contains only air; it is not filled with the medium again, andtherefore cannot be used, until the pump is operated. Filling thecollector circuit with the liquid heat carrier and with air means that,in the event of thermal expansion, an air cushion provides pressureequalization in the collecting container. Freezing and vaporization ofsolar liquid in the outer area are prevented when the solar liquid isemptied out of the collector when the pump is not running. In this caseit is even possible simply to use water as the heat carrier medium,which has the advantage of a greater heat capacity and lower viscositythan glycol/water mixtures. However, this has the disadvantage that thedesign of the collector array is subject to various restrictions becauseof the requirements for filling and emptying, as well as uniform flowthrough it. A minimum gradient is required for the pipe system, as wellas special pumps with a high feed rate and a small throughput, e.g.toothed-wheel pumps, whose operating noise can be highly disturbing.Furthermore, a return vessel is required approximately at the storeheight of the collector circuit inlet, which at the same time must beresistant to temperature and pressure, as well as having particularthermal insulation.

U.S. Pat. No. 4,574,779 describes a solar installation for warm waterproduction, which has a drain-back device with a return section incombination with a heat exchanger. In this case, a store with a pipecoil at the top in a container and the return section vertically belowit are separated by a horizontal separating wall. The pipe coil entersthis from above into the return section, from which solar liquid is fedby means of a pump to the heat consumer or consumers. Solarinstallations such as these involve greater design complexity, becauseof the need for separation of the liquid systems.

DE-A-2 753 756 discloses a solar heating installation which is providedwith an emptying and expansion vessel and is in the form of an opensystem. There is therefore a continuous connection to the atmosphereand, in a corresponding manner, the water level must be continuouslymonitored and added to in order that the heat exchangers for servicewater and heating water do not become dry. Furthermore, thecorresponding components are subject to corrosion attacks.

One important aim of the invention is to overcome the abovementioned andfurther disadvantages of the prior art and to achieve improvements byeconomic means thus allowing a return flow (drain-back) and pressureequalization without an additional external vessel. Novel devices arefurthermore intended to allow volume savings, to be capable of beingmanufactured cost-effectively and also to offer thermodynamic advantageswhich it has not been possible to achieve until now, specifically anincreased heat flow density in the heat exchanging system. A further aimis that the heat storage container should have a longer life and shouldbe better to manufacture.

The main features of the invention are specified in claim 1. Refinementsare the subject matter of claims 2 to 12.

In a solar installation having a collector array which is connected by aforward line and a return line, in places in particular in the form of aline pair, to a heat exchanger of a heat storage container, with thereturn line having a pump, possibly with a bypass for it, and with adrain-back holding device being provided on the forward side or returnside, the invention provides, as claimed in the characterizing part ofclaim 1, that the drain-back holding device is located in the heatstorage container and is physically combined with the heat exchanger,which is in the form of an integral pipe coil and has an expansion andreturn volume in its upper area. There is therefore no need for anexternal expansion vessel, that is to say in the forward line outsidethe store. The volume of the heat carrier medium is designed such that,when the pump is not running, the drain-back holding device is filledwith it, but holds the displaced air during pump operation. When thetemperature rises, this cushions the expansion of the heat carriermedium without the pressure increase associated with this leading topremature response of a safety valve.

A return collecting device has admittedly conventionally previously beenarranged within a store, but as a specifically shaped appliance weldedin upstream of the heat exchanger in the flow direction. In contrast,according to the invention, the return volume that is required isaccommodated directly in the heat exchanger, as a result of which itslower area and its upper area merge seamlessly into one another. Thisdesign simplification as well as the use of pressure-resistant andtemperature-resistant pipe material without any weld beads and withoutinsulation results in particularly simple production with substantialsavings in manufacture, and maintenance simplifications.

Claim 3 provides that a reheating heat exchanger is arranged above thepipe coil in the heat storage container, preferably coaxially with it,with respect to the container axis. This second heat exchanger isconnected to a secondary heater in order to be used as a substitute heatsource in the form of a bivalent store, if solar radiation fails orbecomes weaker.

At least the lower pipe coil area can, according to claim 4, containdevices for reducing the free flow cross section in the interior, forexample one or more filling bodies. This improves the heat transfer. Thetotal heat capacity is also increased if such filling bodies arecomposed of a material with high thermal capacity. While thiscontributes to long-term heat storage, the system responds, however, totemperature changes with somewhat more inertia.

Admittedly, hollow elastic inserts had been provided in heat exchangerpipes in an apparatus according to DE-A-3 315 280, which, as passivefrost protection, allow water volume increases, and which are thereforeintended to prevent heat exchanger pipes in a water cooler from burstingas a result of freezing. However, this has nothing to do with heattransmission.

Furthermore, a solar installation according to the invention makes itpossible to provide for the pump to be a centrifugal pump which isarranged directly under the heat storage container and feeds downward.

In comparison to displacement pumps, centrifugal pumps have a longerlife and produce less noise. Furthermore, flow can pass through themwhen they are stationary. When the pump is stationary, the solar liquidtherefore passes automatically out of the collector back into thedrain-back holding device.

However, cavitation noise can occur in centrifugal pumps, and thecirculation of the storage medium can fail, with air entering thestorage medium because the pump has not been vented and/or because theinput-side water pressure is too low.

According to the invention, the return of the solar heat exchanger inthe store is therefore preferably passed out at the bottom, and the pumpis connected directly to it underneath the store, and is aligned suchthat it first of all feeds directly downward. This arrangementguarantees that, before each start, the pump is completely vented, andcavitation is successfully prevented. Furthermore, this pump arrangementresults in as high a water pressure as possible on the inlet side, sincethe pump is located well below the heat exchanger.

A particularly advantageous refinement of the invention provides for asecond pump to be arranged in the return line. The second pump on theone hand increases the pump power of the overall system, which isadvantageous particularly in the case of a solar collector which is along distance away and is located at a high level. Depending on how highthe collector is installed above the heat storage container on the roof,a very high feed height can result for centrifugal pumps, which extendsto the limit of their performance. In the case of height differencesbetween the store and the collector of more than about 10 m, relativelysmall commercially available centrifugal pumps are no longer adequate.In order to make it possible to dispense with expensive displacementpumps in these situations as well, a second centrifugal pump isconnected to the system in series, according to the invention. While thefirst pump is now arranged at the bottom, the second is preferablyarranged with its pumping direction at the top, after the flow reversalat the store. The second pump is now subject to less stringentrequirements to avoid cavitation, since the inlet side of the secondarypump is already supplied with an increased pressure from the first pump.The electrical drive power which is now required is, however, doubled.

The solar installation can be controlled particularly efficiently if thepumps are connected via a regulating device directly to the collectortemperature sensor and to the store temperature sensor. The regulatingdevice then in each case carries out the control function, and decideswhich of the pumps is operated at what power, depending on thetemperature gradient.

In order to sustainably reduce the constant electricity consumption ofthe overall system, one embodiment of the invention provides that thetwo pumps run jointly only in the starting phase. As soon as the heatstorage medium is circulating constantly, the communicating pipesthroughout the system also result in a suction effect, thus considerablyreducing the feed height power. The invention now provides that, afterthe starting phase, the second pump is switched off by means of theregulating device, in order to reduce the electricity consumption. Thefirst pump then feeds the solar liquid to the solar collector throughthe second pump.

In one development of the solar installation according to the invention,the store temperature sensor is arranged above a sensor terminal stripon the outside of the heat exchanger container. Solutions are known fromthe prior art in which sensor sleeves are introduced into the heatstorage container at a very specific height, through openings.Temperature sensors are then introduced into the heat storage containerthrough these sleeves. This has the disadvantage that every opening mustbe created individually, and must be welded tight with the sleeve. Inthe case of enameled heat storage containers, these openings act asfault points which always represent a corrosion risk. Thesedisadvantages are avoided with the development according to theinvention with the arrangement of the sensor terminal strip.

The sensor terminal strip is composed of metal and is attached to theoutside of the heat storage container via two small, welded-on threadedbolts. One or more store temperature sensors can then be fitted theretoat any desired height. This avoids potential leakage points on sensorsleeves, the height of the store temperature sensor can be chosenfreely, and a plurality of sensors can be fixed to the terminal strip.This likewise avoids penetration in the store insulation, since thestore temperature sensors are laid within the insulation of the heatstorage container.

In the case of a solar installation having a solar collector which isconnected by a forward line and a return line, in places in particularin the form of a line pair, to a heat exchanger of a heat storagecontainer, with the return line having a pump, possibly with a bypassfor it, in particular as claimed in one of claims 1 to 4, independentclaim 5 provides that the heat exchanger is or has a pipe arrangementwhich, according to the invention, is provided with means for reducingthe free flow cross section. Because this results in a reduction in thesolar liquid content, the upper part of the heat exchanger is sufficientto hold the expansion or return volume. Like the collector, the pipearrangement may be a serpentine flat body or else, for example, avertical heater battery, but is preferably in a helical form, with thehelix axis running parallel to the axis of the container. This isbecause the cross section decreases in the pipe interior, as a result ofwhich the pipe external diameter is constant and a uniform standard pipecan be used for manufacture. The bypass is used when the installation isa drain-back system and, at the same time, the pump is a displacementpump which shuts off when the return flow is stationary, preventing thecollector from being emptied.

It is particularly advantageous if, as claimed in claim 6, the pipearrangement is a component of a pipe coil, which guides cylindrical orprofiled filling bodies which therefore reduce the free pipe crosssection, thus leading to an increased flow velocity and therefore tomore turbulence in the pipe system. A pipe can also be used whose volumeis reduced by profiling or cross-sectional reshaping. The increasedturbulence results in an optimum heat transfer. At the same time, therequired heat exchanger volume is less, but can be better utilized,because less heat carrier medium is required and, in the event of atemperature increase, its expansion volume is correspondingly small.There is therefore a considerable difference in comparison to a heatexchanger for sewage installations according to DE-U-1 967 260, whichuses a helix composed of round or flat material for passing a heatingmedium along an inner pipe, which carries slurry, in the form of ahelical line within an outer pipe arranged concentrically with respectto it, in order to achieve better heat transfer by extending the pathlength in this way.

As claimed in claim 7, the filling bodies may have a standard, forexample tubular, form thus allowing them to be produced easily and withadvantageous characteristics, with low costs for manufacture andstorage, specifically with a smooth surface which can slide well. Asclaimed in claim 8, advantageous swirling is achieved by suitably shapedindividual bodies which promote swirling, for example by means of a pipewhich is also wound, singly, during heat-exchanger production. Inparticular, bodies such as these can be closed at the end.

The filling bodies, which can also be introduced into the heat exchangerretrospectively, can be fixed in the pipe coil or, as claimed in claim9, can be guided substantially concentrically therein. However, it isalso possible to use eccentric arrangements and/or filling bodies whichare not rotationally symmetrical.

Further features, details and advantages of the invention will becomeevident from the wording of the claims and from the followingdescription of exemplary embodiments with reference to the drawings, inwhich:

FIG. 1 shows a layout of a solar installation according to theinvention,

FIG. 2 a shows a schematic plan view of a heat exchanger part,

FIG. 2 b shows an enlarged partial side view of a pipe section of theheat exchanger from FIG. 2 a, corresponding to the detail IIb,

FIG. 2 c shows a pipe cross-sectional view relating to FIG. 2 b,

FIG. 3 shows a layout of a solar installation with two pumps and asensor terminal strip, and

FIG. 4 shows an alternative embodiment of a solar installation accordingto the invention.

As can be seen from the schematic overview in FIG. 1, a solarinstallation which is annotated 10 overall has a collector array K whichconsists of two solar collectors 11, 12 which, in the illustratedexample, are in the form of serpentine absorbers. These are connected toa distribution line or bus line 15 which continues on the one hand as aforward path 14 and on the other hand as a return path 16 to a heatstorage container 20, in places in the form of a double-pipe pack 18.

The heat storage container 20 contains a heat exchanger 22, which may bea smooth-pipe helix with a vertical helix axis, and is connected at thebottom to the return path 16, and at the top to the forward path 14. Theupper area of the heat exchanger 22 is in the form of a seamlesstransition as a drain-back holder 24, with the elements 22, 24 formingan integral pipe coil, which is annotated R overall.

A pump 26 is arranged in the return line 16 and can be bridged by abypass 28 for the return flow of the heat carrier medium, which flowsthrough the abovementioned components.

As is indicated by dashed lines, a further heat exchanger 34 can bearranged, in particular coaxially, above the pipe coil R in the heatstorage container 20. It is expediently connected via inlet and outletlines (which are not illustrated) to a heating device (which is likewisenot illustrated) in order to allow reheating in the form of a bivalentsolar store when the solar radiation is relatively low.

As can be seen, the solar installation 10 has a closed collectorcircuit, which is filled predominantly with a heat carrier medium (lineparts shown by thick lines) and partially with air (line and heatexchanger parts which are shown hollow). The volume of the liquid heatcarrier medium is designed such that the helixes in the pipe coil R areapproximately filled with the heat carrier liquid when the pump 26 isnot running. As soon as the pump runs, the upper area 24 of the pipecoil R now holds the displaced air. An air cushion is thus formed which,because of its compressibility, compensates for the volume expansion ofthe heat carrier medium when the temperature rises. Even in the event ofcollector overheating, the volume of vaporized heat carrier liquid canbe accommodated without the pressure increase leading to response for asafety valve, provided that the collectors are arranged horizontally andthe solar liquid vapor pressure forces out the entire collector content,which at the same time prevents vaporization of relatively large amountsof solar liquid.

The pipe coil R is widened by a number of pipe turns, by means of thedrain-back holder 24 which is plugged onto the heat exchanger 22. Thiswould intrinsically require a correspondingly greater amount of the heatcarrier medium. In order to counteract this and at the same time toimprove the heat transfer, the invention provides that means forreducing the cross section are provided at least in the lower area ofthe pipe coil R, that is to say in the heat exchanger 22, for example—asis shown in FIGS. 2 a to 2 c—one or more moving filling bodies 30 and/orfixed installed parts in the pipe interior 32. A tubular body, forexample, or a sequence of individual bodies can be provided, which canalso be introduced retrospectively into the pipe coil R and, ifrequired, can be fixed in it. In the example in FIG. 2 b, a number ofcylindrical filling bodies 30 are provided in the interior 32 of thepipe arrangement and are located one behind the other, at a distancefrom the pipe walls. This reduces the free flow cross section in thepipe mainly in edge areas, as a result of which the flow velocity in theremaining circumferential gap is increased and, at the same time,swirling is produced in a manner known per se.

The filling bodies 30 are, in particular, closed at the end and areprovided with a smooth surface. If they each consist of a pipe piece,then the desired volume displacement is achieved by this pipe piecebeing closed at both ends or open at one end, but being filled with airwhich additionally buffers the thermal expansion. The filling bodies 30may be composed of a material with a high thermal capacity. If they havea profile, for example with radial webs or vanes, this allows or assistspreferred concentric guidance in the pipe interior 32, as is indicatedin FIG. 2 c (with radial supports being omitted). However, provision isalso made for the filling bodies 30 to be guided eccentrically in thepipe interior 32 (FIG. 2 b). Alternatively, it is also possible for thepipe coil to be flattened at defined points, thus likewise increasingthe contact area with the storage medium.

The invention is not restricted to any of the embodiments describedabove but can be modified in many ways. For example, the nature,arrangement and number of the collectors 11, 12 can be varied, as canhydraulics connected thereto. Furthermore, individual pipes can beprovided instead of the double pipe guidance. The lines 14, 15, 16 may,for example, be laid in situ as copper pipes. A pump bypass 28 is notrequired for all applications.

When the pump is stationary, it is desirable for air to rise in theforward path 14. During pump operation, air is prevented from risingtherein by the high flow velocity of the heat carrier medium in thecollector circuit. Moving filling bodies 30 are held against the dynamicpressure of the flowing liquid in the pipe arrangement by means, forexample, of a lower grid insert (which is not shown). Floating up isprevented by the specific gravity of the filling bodies 30 or bysuitable design measures.

Tubular individual bodies 30 can also be incorporated even during theproduction of the heat exchanger 22, by winding of the pipe turns. Ifthe filling bodies 30 have a spherical shape, then they can convenientlybe wound into the complete pipe coil R.

As can be seen, one preferred form of a solar installation 10 with acollector array K and a heat storage container 20 has a drain-backholding device 24 on the forward side or return side which, according tothe invention, is integrated with a heat exchanger 22 located in thestorage container 20, in that its upper area has an expansion and returnvolume. An integral pipe coil R is advantageous, particularly asmooth-pipe helix with a uniform gradient. Furthermore—as in the case ofbivalent solar stores—a second reheating heat exchanger 34, which iscoaxial with it with respect to the container axis, can be provided. Atleast in the lower area of the pipe coil R, that is to say in the heatexchanger 22, means are provided for reducing the free flow crosssection in the pipe interior 32, specifically cylindrical or profiled,preferably moving, filling bodies 30. In particular, these may becomposed of a material of high thermal capacity, for example of steel,stone, ceramic or the like. The filling bodies 30 are expedientlyindividual bodies with a standard form, which in particular promotesswirling. A single filling body 30 is also possible, for example a steelpipe which is closed at the end.

In addition to the features known from FIG. 1, FIG. 3 shows a secondpump 27. The figure also shows that both pumps 26, 27 are connected viaa regulating device 40 to the collector temperature sensor 44 and to thestore temperature sensors 42. The store temperature sensors 42 are inthis case arranged on a sensor terminal strip 50. The sensor terminalstrip is attached to the heat storage container 20 by means of threethreaded bolts 52. The sensor terminal strip 50 is in this case alsolocated, together with the store temperature sensors 42, within theinsulation. The pump 26 is a centrifugal pump which is arranged directlyunder the heat storage container, and feeds downward. The second pump 27feeds upward, and is likewise in the form of a centrifugal pump.

FIG. 4 shows a modification of the solution shown in FIG. 3. In thiscase, the pump 26 is in the form of a displacement pump. The bypass 28is therefore provided, and is likewise connected to the regulatingdevice 40.

All the features and advantages, including design details, spatialarrangements and method steps, which are mentioned in the claims, thedescription and the drawings may be significant to the invention both intheir own right and in the most widely differing combinations.

LIST OF REFERENCE SYMBOLS

K Collector array

R Pipe coil

10 Solar installation

11, 12 Solar collectors

14 Forward line

15 Distribution/collecting line

16 Return line

18 Line pair

20 Heat storage container

22 Heat exchanger/lower area

24 Drain-back holder/upper area

26 Pump

27 Second pump

28 Bypass

30 Filling body

32 Pipe interior

34 Reheating heat exchanger

40 Regulating device

42 Store temperature sensor

44 Collector temperature sensor

50 Sensor terminal strip

52 Threaded bolt

1. A solar installation (10) having a collector array (K) which isconnected by a forward line (14) and a return line (16), in places inparticular in the form of a line pair (18), to a heat exchanger (22) ofa heat storage container (20), with the return line (16) having a pump(26), possibly with a bypass (28) for it, and with a drain-back holdingdevice (24) being provided on the forward side or return side, whereinthe drain-back holding device (24) is located in the heat storagecontainer (20) and is physically combined with the heat exchanger (22),which is in the form of an integral pipe coil and has an expansion andreturn volume in its upper area.
 2. The solar installation as claimed inclaim 1, wherein the pipe coil (R) is a smooth-pipe helix with a uniformgradient.
 3. The solar installation as claimed in claim 1, wherein areheating heat exchanger (34) is arranged above the pipe coil (R) in theheat storage container (20), preferably coaxially with respect to it. 4.The solar installation as claimed in claim 1, wherein at least the lowerarea of the pipe coil (R) contains devices for reducing the free flowcross section in the interior, for example one or more filling bodies(30).
 5. The solar installation as claimed in claim 1, wherein the pump(6) is a centrifugal pump which is arranged directly under the heatstorage container and feeds downward.
 6. The solar installation asclaimed in claim 1, wherein a second pump (27) is arranged in the returnline (16).
 7. The solar installation as claimed in claim 1, wherein thepumps (26, 27) are connected via a regulating device (40) to thecollector temperature sensor (44) and to at least one store temperature(42).
 8. The solar installation as claimed in claim 1, wherein the storetemperature sensor (42) is arranged above a sensor terminal strip (50)on the outside of the heat exchanger container (20).
 9. The solarinstallation as claimed in claim 1, wherein the heat exchanger (22) isor has a pipe arrangement which is provided in its interior (32) withmeans for reducing the free flow cross section.
 10. The solarinstallation as claimed in claim 9, wherein the pipe arrangement is acomponent of a pipe coil (R), which guides cylindrical or profiledfilling bodies (30) in the interior (32), at least in its lower area(22).
 11. The solar installation as claimed in claim 10, wherein thefilling bodies are in a standard, for example tubular, form.
 12. Thesolar installation as claimed in claim 10, wherein the filling bodies(30) are individual bodies which in particular are closed at the end andpromote swirling.
 13. The solar installation as claimed in claim 10,wherein the filling bodies (30) are guided substantially concentricallyin the pipe coil (R).